Leffler died after crashing during the first heat at Bridgeport Speedway, a dirt track about 15 miles southwest of Philadelphia. A spectator, Chris Taitt, said he was at the race but looking the other way when the crash occurred. He said Leffler had been in second place, apart from other cars when his car slammed into a wall.

Leffler, 37, a native of Long Beach, Calif., won twice in the Nationwide series and finished in both the Indianapolis 500 and the Daytona 500, two of racing's signature events. But apart from a last-place finish in Sunday's NASCAR race at Pocono, he had spent most of 2013 racing on dirt tracks.

"Jason Leffler was a great racer and an even better friend," said Sprint Cup driver Tony Stewart, once a teammate of Leffler's at Joe Gibbs Racing. "To not have him around to talk about whatever race one of us had just run, or were going to run, will be hard. My thoughts and prayers go out to his family, especially his son, Charlie, who Jason loved more than anything."